About Environment Variables
SHORT DESCRIPTION
Describes how to access Windows environment variables in PowerShell.
LONG DESCRIPTION
Environment variables store information about the operating system environment. This information includes details such as the operating system path, the number of processors used by the operating system, and the location of temporary folders.
The environment variables store data that is used by the operating system and
other programs. For example, the WINDIR
environment variable contains the
location of the Windows installation directory. Programs can query the value of
this variable to determine where Windows operating system files are located.
PowerShell can access and manage environment variables in any of the supported operating system platforms. The PowerShell environment provider simplifies this process by making it easy to view and change environment variables.
Environment variables, unlike other types of variables in PowerShell, are inherited by child processes, such as local background jobs and the sessions in which module members run. This makes environment variables well suited to storing values that are needed in both parent and child processes.
Using and changing environment variables
On Windows, environment variables can be defined in three scopes:
- Machine (or System) scope
- User scope
- Process scope
The Process scope contains the environment variables available in the current process, or PowerShell session. This list of variables is inherited from the parent process and is constructed from the variables in the Machine and User scopes. Unix-based platforms only have the Process scope.
You can display and change the values of environment variables without using a cmdlet by using a variable syntax with the environment provider. To display the value of an environment variable, use the following syntax:
$Env:<variable-name>
For example, to display the value of the WINDIR
environment variable, type
the following command at the PowerShell command prompt:
$Env:windir
In this syntax, the dollar sign ($
) indicates a variable, and the drive name
(Env:
) indicates an environment variable followed by the variable name
(windir
).
When you change environment variables in PowerShell, the change affects only
the current session. This behavior resembles the behavior of the Set
command
in the Windows Command Shell and the Setenv
command in UNIX-based
environments. To change values in the Machine or User scopes, you must use the
methods of the System.Environment class.
To make changes to Machine-scoped variables, must also have permission. If you try to change a value without sufficient permission, the command fails and PowerShell displays an error.
You can change the values of variables without using a cmdlet using the following syntax:
$Env:<variable-name> = "<new-value>"
For example, to append ;c:\temp
to the value of the Path
environment
variable, use the following syntax:
$Env:Path += ";c:\temp"
On Linux or MacOS, the colon (:
) in the command separates the new path from
the path that precedes it in the list.
$Env:PATH += ":/usr/local/temp"
You can also use the Item cmdlets, such as Set-Item
, Remove-Item
, and
Copy-Item
to change the values of environment variables. For example, to use
the Set-Item
cmdlet to append ;c:\temp
to the value of the Path
environment variable, use the following syntax:
Set-Item -Path Env:Path -Value ($Env:Path + ";C:\Temp")
In this command, the value is enclosed in parentheses so that it is interpreted as a unit.
Environment variables that store preferences
PowerShell features can use environment variables to store user preferences. These variables work like preference variables, but they are inherited by child sessions of the sessions in which they are created. For more information about preference variables, see about_preference_variables.
The environment variables that store preferences include:
PSExecutionPolicyPreference
Stores the execution policy set for the current session. This environment variable exists only when you set an execution policy for a single session. You can do this in two different ways.
Start a session from the command line using the ExecutionPolicy parameter to set the execution policy for the session.
Use the
Set-ExecutionPolicy
cmdlet. Use the Scope parameter with a value of "Process".For more information, see about_Execution_Policies.
PSModuleAnalysisCachePath
PowerShell provides control over the file that is used to cache data about modules and their cmdlets. The cache is read at startup while searching for a command and is written on a background thread sometime after a module is imported.
Default location of the cache is:
- Windows PowerShell 5.1:
$env:LOCALAPPDATA\Microsoft\Windows\PowerShell
- PowerShell 6.0 and higher:
$env:LOCALAPPDATA\Microsoft\PowerShell
- Non-Windows default:
~/.cache/powershell
The default filename for the cache is
ModuleAnalysisCache
. When you have multiple instances of PowerShell installed, the filename includes a hexadecimal suffix so that there is a a unique filename per installation.Note
If command discovery isn't working correctly, for example Intellisense shows commands that don't exist, you can delete the cache file. The cache is recreated the next time you start PowerShell.
To change the default location of the cache, set the environment variable before starting PowerShell. Changes to this environment variable only affect child processes. The value should name a full path (including filename) that PowerShell has permission to create and write files.
To disable the file cache, set this value to an invalid location, for example:
# `NUL` here is a special device on Windows that cannot be written to, # on non-Windows you would use `/dev/null` $env:PSModuleAnalysisCachePath = 'NUL'
This sets the path to the NUL device. PowerShell can't write to the path but no error is returned. You can see the errors reported using a tracer:
Trace-Command -PSHost -Name Modules -Expression { Import-Module Microsoft.PowerShell.Management -Force }
- Windows PowerShell 5.1:
PSDisableModuleAnalysisCacheCleanup
When writing out the module analysis cache, PowerShell checks for modules that no longer exist to avoid an unnecessarily large cache. Sometimes these checks are not desirable, in which case you can turn them off by setting this environment variable value to
1
.Setting this environment variable takes effect immediately in the current process.
PSModulePath
The
$env:PSModulePath
environment variable contains a list of folder locations that are searched to find modules and resources.By default, the effective locations assigned to
$env:PSModulePath
are:System-wide locations: These folders contain modules that ship with PowerShell. The modules are store in the
$PSHOME\Modules
location. Also, This is the location where the Windows management modules are installed.User-installed modules: These are modules installed by the user.
Install-Module
has a Scope parameter that allows you to specify whether the module is installed for the current user or for all users. For more information, see Install-Module.- On Windows, the location of the user-specific CurrentUser scope is
the
$HOME\Documents\PowerShell\Modules
folder. The location of the AllUsers scope is$env:ProgramFiles\PowerShell\Modules
. - On non-Windows systems, the location of the user-specific CurrentUser
scope is the
$HOME/.local/share/powershell/Modules
folder. The location of the AllUsers scope is/usr/local/share/powershell/Modules
.
- On Windows, the location of the user-specific CurrentUser scope is
the
In addition, setup programs that install modules in other directories, such as the Program Files directory, can append their locations to the value of
$env:PSModulePath
.For more information, see about_PSModulePath.
Managing environment variables
PowerShell provides several different methods for managing environment variables.
- The Environment provider drive
- The Item cmdlets
- The .NET System.Environment class
- On Windows, the System Control Panel
Using the Environment provider
Each environment variable is represented by an instance of the System.Collections.DictionaryEntry class. In each DictionaryEntry object, the name of the environment variable is the dictionary key. The value of the variable is the dictionary value.
To display the properties and methods of the object that represents an
environment variable in PowerShell, use the Get-Member
cmdlet. For example,
to display the methods and properties of all the objects in the Env:
drive,
type:
Get-Item -Path Env:* | Get-Member
The PowerShell Environment provider lets you access environment variables in a
PowerShell drive (the Env:
drive). This drive looks much like a file system
drive. To go to the Env:
drive, type:
Set-Location Env:
Use the Content cmdlets to get or set the values of an environment variable.
PS Env:\> Set-Content -Path Test -Value 'Test value'
PS Env:\> Get-Content -Path Test
Test value
You can view the environment variables in the Env:
drive from any other
PowerShell drive, and you can go into the Env:
drive to view and change the
environment variables.
Using Item cmdlets
When you refer to an environment variable, type the Env:
drive name followed
by the name of the variable. For example, to display the value of the
COMPUTERNAME
environment variable, type:
Get-ChildItem Env:Computername
To display the values of all the environment variables, type:
Get-ChildItem Env:
Because environment variables do not have child items, the output of Get-Item
and Get-ChildItem
is the same.
By default, PowerShell displays the environment variables in the order in which
it retrieves them. To sort the list of environment variables by variable name,
pipe the output of a Get-ChildItem
command to the Sort-Object
cmdlet. For
example, from any PowerShell drive, type:
Get-ChildItem Env: | Sort Name
You can also go into the Env:
drive by using the Set-Location
cmdlet:
Set-Location Env:
When you are in the Env:
drive, you can omit the Env:
drive name from the
path. For example, to display all the environment variables, type:
PS Env:\> Get-ChildItem
To display the value of the COMPUTERNAME
variable from within the Env:
drive, type:
PS Env:\> Get-ChildItem ComputerName
Saving changes to environment variables
To make a persistent change to an environment variable on Windows, use the System Control Panel. Select Advanced System Settings. On the Advanced tab, click Environment Variable.... You can add or edit existing environment variables in the User and System (Machine) scopes. Windows writes these values to the Registry so that they persist across sessions and system restarts.
Alternately, you can add or change environment variables in your PowerShell profile. This method works for any version of PowerShell on any supported platform.
Using System.Environment methods
The System.Environment class provides GetEnvironmentVariable and SetEnvironmentVariable methods that allow you to specify the scope of the variable.
The following example uses the GetEnvironmentVariable method to get the
machine setting of PSModulePath
and the SetEnvironmentVariable method
to add the C:\Program Files\Fabrikam\Modules
path to the value.
$path = [Environment]::GetEnvironmentVariable('PSModulePath', 'Machine')
$newpath = $path + ';C:\Program Files\Fabrikam\Modules'
[Environment]::SetEnvironmentVariable("PSModulePath", $newpath, 'Machine')
For more information about the methods of the System.Environment class, see Environment Methods.